Mystery of the dead quarantined clown fish

I woke up this morning and found two ocellarris clown fish dead in my quarantine tank. They had been in there for 5 days with no other fish and appeared to be healthy and were eating well. I found one laying on the aquarium bottom and one had been sucked onto the hang on the back filtration strainer. I am stumped on what killed them. After removing them I did a water test of the quarantine tank and discovered the following:

Hydrometer: 1.024
PH: 7.8
Ammonia: 0.25
Nitrite: 0ppm
Nitrate: 0ppm
Temperature: 76 F

My quarantine tank has been set up for 2 months now and is a 10 gallon tank with a Marineland bio wheel hang on the back filter, a cave and an in tank heater. I also have live sand, which I was planning on replacing (after receiving advice from my LFS) with live rock after the clown fish had completed there quarantine process. I have only used the quarantine tank one other time before for a red fin wrasse, who remained there for two weeks prior to being introduced into my main tank. This fish is still doing very well. My last 25% water change in the quarantine tank was completed 2 weeks ago.

Does anyone have any ideas or advise on what may have caused this, and how to prevent this from occurring in the future.

V/R

Chris

 

any sign of wounds on the fish?

 

Welcome to 3reef Chris.

Ammonia was present, to keep the nitrifying bacteria up to par you need to feed them.

You did a great job on the the QT and the seeded filter, but you needed to continue to ghost feed the biological filter /bacteria to keep their numbers up to par to be able to keep up with the new additions and their feeding requirements.

Certainly sounds like you have a good program with regard to the QT. You may have purchased clowns already infected with lethal pathogens such as Brookynella.

The biological filter is ever evolving, if not provided with biological material that continues the nitrogen cycle, the cycle stops or slows down and can not keep up.